As known in the art, an admixture is a material other than hydraulic cement, water and aggregate that is used as an ingredient of concrete or mortar and is added to the batch immediately before, during or after its mixing. Admixtures are used to modify the properties of the concrete in such a way as to make it more suitable for a particular purpose or for economy. Thus, the major reasons for using admixtures are (1) to achieve certain structural improvements in the resulting cured concrete; (2) to improve the quality of concrete through the successive stages of mixing, transporting, placing, and curing during adverse weather or traffic conditions; (3) to overcome certain emergencies during concreting operations; and (4) to reduce the cost of concrete construction. In some instances, the desired result can only be achieved by the use of an admixture. In addition, using an admixture allows the employment of less expensive construction methods or designs and thereby offsets the costs of the admixture.
For one example of an application of an admixture for use in concrete, at the end of a delivery, concrete mixers may contain from 200 to 600 pounds of residual cement, sand or rock. When left in the mixer overnight, the residual concrete will settle and harden in the bottom of the mixer. While the residual materials can be washed out of the mixer with a large amount of water, disposal of the liquid may cause an environmental problem, particularly in large metropolitan areas. To avoid this problem, it is desirable to stabilize the setting of residual concrete in a mixer so that it remains fluid and the residual material can still be used the next day. It is also desirable to be able to stabilize the setting of concrete in a mobile mixer while the mixer is being transported to another location. For specific applications, it may also be desirable to stabilize the setting of concrete for a specific length of time, during breakdown or delay in traffic in populated areas. The addition of retarding admixture to the concrete is used to solve each of these problems. By varying the amounts of a retarding admixture used in a batch, the setting of the concrete can be delayed for a selected time period.
A stabilizer completely inhibits the setting formation of concrete for a predetermined period of time depending upon the amount of stabilizer added. A stabilizer is defined as an admixture that stops or slows down the hydration process of both silicate and aluminate phases of Portland cement; causes a controlled decrease of the rate of hydration of hydraulic cement, and lengthens the time of setting in both freshly batched concrete for long hauls and returned concrete for reuse; and stops the hydration of cement in washwater allowing it to be reused the next day. As such, a stabilizer stops the cement hydration process, whereas a retarder delays the concrete setting process. Along with the aforementioned advantages, stabilizers also provide improved workability, reduced segregation, superior finishing characteristics, flexibility in scheduling placing and finishing operations, elimination of cold joints and reductions in thermal cracking. Use of a stabilizer also reduces or eliminates the need for portable batch plants necessary to service long distance jobs. When mixed with plastic concrete, the stabilizer stops cement hydration by forming a protective barrier around cementitious particles. This barrier prevents portland cement, fly ash and granulated slag from achieving initial set. Such a stabilizer is currently sold under the tradename DELVO by Master Builders, Inc., Cleveland, Ohio, the assignee of the present invention.
The amount of stabilizer to be added to a batch of concrete is determined by numerous factors. These factors include, but are not limited to, the amount and temperature of the concrete, the amount of accelerant and retarder added to the concrete and the age of the concrete. Stabilizers may be used for the stabilization of unused concrete returned from a job site, stabilization of concrete that must travel extended distances to a job site and for "washing-out" any residue contained in empty trucks which may then be used in a new batch of concrete. To return the stabilized concrete to its normal setting condition, an activator may be added to the concrete batch. Thus, if a batch of stabilized concrete is delivered to a job site with another two hours remaining in the stabilization period, an activator may be added to begin the concrete setting process immediately.
Difficulties arise in the use of stabilizers due to their precise quantity requirements. These difficulties are primarily attributable to the various factors that must be considered. These factors include, but are not limited to, the other chemical admixtures, concrete materials and mix designs used; the elapsed time from initial batching; the returned plastic concrete temperature; the quantity of concrete being treated; and the stabilization time required. In the past, charts with the various factors were employed to determine the amount of stabilizer to mix with the concrete. For example, if unused, returned plain concrete is to be used that same day, the batchman must first determine the temperature of the concrete and how much accelerator or retarder has been added. Next, the batchman must determine the age of the unused concrete within the half-hour. Usually, concrete older than 3.5 hours cannot be treated. Next, the batchman must determine for how long the treated concrete is to be stabilized. Based on these factors a stabilizer amount is determined for a given quantity of concrete. The calculated amount of stabilizer then is added and mixed for 5-7 minutes.
Unfortunately, the aforementioned charts may be misread or, alternatively provide exaggerated quantity amounts if an improper factor value is used. If too little stabilizer is mixed with a batch of concrete it begins to set before arriving at a job site, making the concrete unusable. If too much stabilizer is added, the setting process is delayed and interferes with construction schedules and the like. As a result, concrete mixers and suppliers are dissatisfied with the performance of stabilizers and may be disinclined to use them.
As seen above, the successful use of admixtures depends upon the accuracy with which they are prepared and batched. Batching means the weighing or volumetric measuring of the ingredients for a batch of either concrete or mortar and introducing them into the mixer. The amount of admixture added during batching must be carefully controlled. Inaccuracies in the amount of admixture added can significantly affect the properties and performance of the concrete being batched and even defeat the original purpose of including the admixture. The need for accuracy in measuring the amount of solid or even liquid admixture to be added to a batch is particularly acute where only a relatively small amount of admixture is required for the job. Accordingly, it is desirable to have a system and related method of dispersing admixture which is accurate, saves time and optimizes the reclamation of unused concrete for a fleet of mixer trucks.
U.S. Pat. Nos. 4,964,917; 5,203,919; and 5,427,617 to Bobrowski et al, which are assigned to the assignee of the present invention, disclose methods and compositions for reclaiming and stabilizing concrete with the use of hydration retarding agents, stabilizing agents and acceleration agents. The concrete is reclaimed by retarding or stabilizing the hydration of the unused portion returned from a job site by adding a retarding or stabilizing agent and at the end of the retardation period, diluting the retarded concrete with fresh concrete. Factors such as time, temperature, the type of new concrete, the type of returned concrete and the like are considered in determining how to treat the unused concrete.
U.S. Pat. No. 5,268,111 to Metz et al discloses a concrete reclamation system with a mixing agitator. The unused concrete is placed in a receiving tank with diluting solution of water. After thorough mixing, the sand and aggregate components of the concrete settle into a first layer and the cement solids and a fines portion of the sand settle into a second water-mixture layer. The layers are then separated and conveyed to respective storage areas for later use. The disclosures of U.S. Pat. Nos. 4,964,917; 5,203,919; 5,427,617; and, 5,268,111 are incorporated herein as if fully written out below.
Although the above noted patents describe methods to reclaim and stabilize concrete, the difficulties involved with using stabilizers and other admixtures present certain disadvantages. In particular, the patent to Metz et al employs a cumbersome aggregate separation system that is simply not required by use of the present invention. The industry does not currently have a system for calculating the precise amount of admixture to be added for new or unused concrete. Nor is it known to precisely control the dispensing of the admixture, such as stabilizers, with the same system. Another deficiency of the known art is that no known system can manage an entire fleet of concrete mixing trucks with respect to the deposition of admixtures, on site or remotely, to ensure that trucks with unused concrete are reclaimed prior to using empty trucks.
Other difficulties which are not addressed by the above patents include the generation of reports related to the status of the mixing trucks, how much concrete is saved by using the system, and the like. Also, the ease of determining and dispensing the appropriate admixtures are not addressed by the above patents.
It is therefore an object of the present invention to provide an admixture dispensing and concrete mixer monitoring system for monitoring the content status of concrete mixers. Another object of the present invention is to provide a system for easily determining the nature and amount of admixture that needs to be included with the other concrete ingredients and controlling the dispensing of the same, which streamlines the efficient use of a fleet of delivery trucks and saves time and material costs in the manufacture of concrete.